In the present circumstances, where efforts are being undertaken to reduce amounts of discharged carbon dioxide which promotes global warming, and bright LEDs exhibiting high luminous efficiency have come into practical use, LEDs (light emitting diodes, semiconductor light sources) with low power consumption are starting to become more popular in place of conventional tungsten filament light bulbs as light sources of vehicle light fixtures. The LED has a long life and can be controlled simply by supplying a constant current thereto so as to emit a stable brightness, and therefore the LED can be used favorably as a light source of a vehicle light fixture. Moreover, the output (the luminous intensity) of LEDs has increased in recent years, and as a result, LEDs are starting to become more popular as light sources for vehicle-mounted headlamps.
Note that, a vehicle-mounted headlamp, and in particular a low-beam lamp, differs from an usual illumination lamp, a light distribution unique to vehicle-mounted use is required with which drivers of oncoming vehicles are not dazzled, or in other words, with which light is not emitted into the eyes of drivers of oncoming vehicles (i.e. a light distribution with which the positions corresponding to the eyes of drivers of oncoming vehicles become dark).
A conventional example of this type of vehicle-mounted headlamp, in which a low-beam lamp light distribution is formed by providing a light distribution member between an LED and a projector lens and the light emitted by the LED is used effectively, will be described below.
In a vehicle-mounted headlamp according to Patent Document 1, as shown in FIGS. 4 and 9 of Patent Document 1, a low-beam lamp light distribution is formed by a first reflecting surface provided on an optical axis, while light emitted upward by an LED is guided frontward by a second reflecting surface provided above the optical axis, and thereby used effectively.
In this configuration, light emitted downward from the LED is reflected by the first reflecting surface, but the reflected light travels toward the second reflecting surface and is then reflected repeatedly between the two reflecting surfaces so that the light attenuates. Therefore, room for improvement remains with respect to effective use of the light emitted by the LED.
Further, in a configuration shown in FIG. 11 of Patent Document 1, light emitted frontward by the LED enters through an incident surface of an optical member having a function of a convex lens, while the light emitted upward by the LED is guided frontward through being reflected by a convex surface-shaped reflecting surface that forms an inner surface of the incident surface.
In this configuration, the light emitted downward from the LED leaks out, so that room for improvement remains with respect to effective use of the light emitted by the LED.
An optical unit for a vehicle according to Patent Document 2 does not relate to a headlamp, but includes a light incident portion and a reflecting surface for guiding light emitted around from an LED to an exit surface without allowing the light to escape. When this configuration is employed as it is, however, it is impossible to form a light distribution for a headlamp in which a particular light distribution is required.